Method of heating tunnel kilns and a tunnel kiln for carrying the method into effect



Nov. 24, 1964 G. CREMER ETAL 3,158,364

.METHOD OF HEATING TUNNEL KILNS AND A TUNNEL KILN FOR CARRYING THE METHOD INTO EFFECT Filed June 30. 1961 2 Sheets-Sheet 1 GOTTFRIED CREMER HEINZ BEHRENS Warm mm ATTORN EY NOV. 1954 G. CREMER ETAL 3,158,364

METHOD OF HEATING TUNNEL KILNS AND A TUNNEL KILN FOR CARRYING THE METHOD INTO EFFECT Filed June 30, 1961 2 Sheets-Sheet 2 GOTTFRIED CREMER HElNZ BEHRENS 5072M m Jwon ATTOR N EY United States Patent 3,158,364 METHOD GE HEATING TUNNEL KELNS AND A TUNNEL KEEN FUR CARRYENG THE METHQD INTO EFFECT Gottfried Qremer, Steyrerweg 6, @ologne-iunlrersdorf,

Germany, and Heinz Behrens, Hauptstrasse 2i), Schwarzenfeld, ()berpfaiz, Germany Filed dune 30, 1961, der. No. 121,135 Claims priority, application Germany .luly 5, 19st? 9 Claims. (Cl. 263-2d) The invention relates to a method of heating tunnel kilns with gas or atomising burners which, although not in any way restricted to this particular application, has the special advantage that it permits the satisfactory heat ing of tunnel kilns of great width, as are now preferred due to the trend of recent developments.

It is known that gas or oil atomising burners give a particularly good efiiciency of combustion. As regards their use in tunnel kilns, however, they have the drawback that a comparatively high temperature is developed at the burner outlet so that it becomes difiicult, if not impossible, to obtain an even distribution of temperature over the entire width of the tunnel kiln and thereby over the cross-section of the material to be baked and moved through the tunnel kiln.

When building tunnel kilns of comparatively great width, i.e. where the problem of even temperature distribution is still more difficult to solve, impulse burners are employed. In these impulse burners, the oil or other liquid fuel is injected, or more precisely flung, in portions into the combustion chamber, the individual portions of the liquid fuel being burned away on their way from the burner outlet to a point of impingement located at a distance from the burner, for example on the opposite side of the kiln from the latter. With this type of burner, it is not only possible to bridge considerable widths of kiln but the burner outlet is also very largely protected from excessive temperature effects, since the burning away of the injected or flung-in portions of the oil commences only at some distance from the burner outlet. In this manner an exceptionally good temperature distribution is obtained over the cross-section of the kiln.

In View of the fact that these impulse burners, as has been explained above, do not atomise the oil, it is inevitable that when the latter issues from the jets or nozzles significant amounts of oil drip down, these oil drippings resulting in fouling of the combustion chambers and influencing the atmosphere in the kiln adversely owing to uncontrolled after-combustion. Accordingly, with this type of heating system, special precautions must be taken to render the effects of this dripping as harmless as possible.

The object of the present invention is to provide a kiln in which the disadvantages inherent in both of the aforesaid heating systems are avoided and the invention proposes, in the heating of tunnel kilns by means of gaseous or atomised liquid fuels, that the fuel be introduced,

for example injected or atomised, in a manner known.

per se without the admixture of a combustion-maintaining gas, for example air, and that the gas which first renders possible and maintains the combustion process be blown or injected into the combustion chamber in spatially separated streams, but substantially parallel to the streams of fuel.

It is known to inject the fuel into the combustion chamber without the admixture of air, the supply of air being effected by means of an air conduit surrounding the burner jet, so that the air and fuel are mixed substantially immediately after the exit of the fuel from the jet. Here again, however, the disadvantage mentioned at the outset arises, namely that undesirable high temperatures occur in the immediate vicinity of the burner jet, so that even temperature distribution over the width of the kiln is not obtainable with any degree of certainty.

In the method of heating according to the invention, in which the gas rendering possible and maintaining the combustion process is blown in streams separated spatially from the jets of fuel, the high temperatures in the burner jet which are unavoidable in atomising burners are firstly avoided, in fundamental contrast to the known heating methods, since the combustion of the fuel takes place only when the air or other gas rendering possible and maintaining the combustion process comes into contact with the atomised fuel at a given distance from the burner jet. Secondly, dripping of liquid fuel at the burner jet is also avoided, since the liquid fuel issues from the burner jet at high pressure in a finely atomised stream or jet with the avoidance of the formation of droplets at the said burner jet.

Preferabl in the method according to the invention, fuel andthe gas maintaining the combustion thereof are injected substantially horizontally. The method of heating according to the invention may be varied by introducing fuel and air into the combustion chamber at different velocities. Moreover the method of heating according to the invention may also be modified by so inclining the jet of fuel with respect to the stream of air adjacent thereto that the point of intersection of the directions of flow occurs at any desired point within the combustion chamber, but is preferably located substantially at the opposite limit of the combustion chamber.

In a tunnel kiln heated by the method according to the invention, spaces may be provided in a manner known per se on the baking trucks and the burners may direct their jets of fuel into these spaces. According to a further feature of the invention the burners and the feed devices for the gas maintaining the combustion are arranged side by side in the tunnel kiln, the spaces provided on the baking truck or in the charge serving in each case for receiving alternately a jet of fuel and a stream of air and the contact of these tWo media required for the heating being established at the separate ducts or passages receiving them by means of orifices in the partition Walls. The partition walls themselves may be constructed as separate elements, for example auxiliary baking means. They may, however, also be formed by suitably positioned material which is to be baked.

The method according to the invention is suitable, with particular advantage, for tunnel kilns having burners arranged in the side walls of the furnace and directed horizontally into the combustion chamber and with spaces provided on the baking truck below the charge, an air feed device being provided between each pair of burners and the spaces below the charge forming ducts or p assages which are provided with orifices longitudinally of the tunnel kiln. It is also possible, of course, for the partition walls of the ducts to be formed by parts of the charge itself.

Methods of carrying the invention into effect are illustrated in the accompanying drawings, in which:

FIGURE 1 is a vertical cross-section through a tunnel kiln in accordance with the invention,

FIGURE 2 is a section through the tunnel kiln according to FIGURE 1 substantially on the line 1-1, FIGURE 20 is a fragmentary'sectional view of a tunnel kiln similar to that shownin FIGURE 2 illustrating a modified form of the invention, and p FIGURE 3 illustrates another constructional form of baking truck for use-in a tunnel kiln heated in accordance with the invention.

In FlGURE 1 there are indicated at 1 and 2 the side walls of the tunnel kiln, in which a baking truck 3 is transported. The baking truck is transported intermittently or continuously by devices known per se through the intermediary of wheels 4, 5 running on rails 6, 7 arranged in the tunnel kiln.

Apertures 8 in which the burners 9 are accommodated are provided in the side walls 1, 2 of the tunnel kiln. As will be seen from FIGURE 2, the burners 9 alternate with air feed devices 10 and are preferably provided on both sides of the tunnel kiln. The baking truck 3 carries a plurality of auxiliary baking means 11, 12 and 13 on which the charge, i.e. the material to be baked 14, is stacked. Owing to the auxiliary baking means 11, 12 and 13, a space is formed below the charge 14 and into this space the burners 9 inject their fuel. In the known tunnel kilns, this fuel is mixed with air, so that a flame burns at the burner orifice. Due to such known arrangement, a very high temperature is produced at the burner orifice which not only damages the burner but also makes the attainment of an even temperature distribution over the entire cross-section of the kiln impossible.

In the heating system according to the invention, on the other hand, the fuel is injected by the burner 9 practically unmixed with air and the air for combustion is introduced, spatially separated therefrom, through the devices 10. In this Way, the fuel is mixed'with the air for combustion only at a distance within the inner limits of the side walls of the tunnel kiln and substantially even burning is obtained in the space 15.

Of course, the invention does not exclude the fuel being injected mixed with a part of the air required for combustion, the so-called primary air, which generally does not ensure complete combustion of the fuel, so that the addition of larger amounts of secondary air is always required. This embodiment of a system of heating tunnel kilns is obviously also within the scope of the present invention.

FIGURE 2a illustrates a modified embodiment of the structure of FIGURES 1 and 2 wherein the apertures 8' in which the burners or fuel injectors 9' are disposed are spatially separated from and inclined with respect to the air feed devices 10. The relative disposition of the fuel injectors 9' and the air feed devices 10 are such that the direction of flow of fuel and air intersect at a point with in the combustion chamber or space 15 of the tunnel kiln.

FIGURE 3 illustrates a somewhat modified and particularly advantageous embodiment of the structure of the auxiliary baking means on the baking truck 3. As will be seen, in this case partition walls 16 are built up on the baking truck, said partition walls having orifices at 17. In this form of construction, the meeting of the necesary air for combustion with the fuel takes place in a welldefined manner and hence the possibility is provided of controlling the combustion process exactly in the desired manner.

Particularly in this embodiment of the heating system according to the invention, it is possible to inject the fuel already mixed with a proportion of the air for combustion. There are also indicated at 9 and 10 in FIGURE 3 the burners and the air feed devices, respectively.

We claim:

1; A method of heating tunnel kilns which comprises introducing pulses of fuel thereby forming spaced discontinuous streams thereof without substantial admixture of a combustion-maintaining gas into the combustion chamberof the tunnel kiln, and introducing gas for main.- taining combustion into the combustion chamber in streams spatially separated from and substantially parallel to the streams of fuel.

2. A method of heating tunnel kilns which comprises introducing pulses of fuel thereby forming spaced discontinuous streams thereof Without substantial admixture of a combustion-maintaining gas into the combustion chamber of the tunnel kiln, and introducing gas for maintaining combustion into the combustion chamber in streams spatially separated from and substantially parallel to the streams of fuel from points spatially separated 4 from the fuel-introduction points and arranged side by side with the latter so as to alternate therewith.

3. A method of heating tunnel kilns which comprises introducing pulses of fuel thereby forming spaced discontinuous streams thereof without substantial admixture of a combustion-maintaining gas into the combustion chamber of the tunnel kiln, and introducing gas for maintaining combustion into the combustion chamber in streams spatially separated from and substantially parallel to the streams of fuel and at a different velocity from the-latter.

4. A method of heating tunnel kilns which comprises introducing pulses of fuel thereby forming spaced discontinuous streams thereof without substantial admixture of a combustion-maintaining gas into the combustion chamber of the tunnel kiln, and introducing gas for maintaining combustion into the combustion chamber in streams spatially separated from and inclined with respect to the streams of fuel such that the directions of flow intersect at points within the combustion chamber.

5. A method according to claim 4, wherein the points of intersection of flow of said streams are located substantially at the opposite limit of the combustion chamber from the points of introduction.

6. A method of heating tunnel kilns which comprises introducing pulses of fuel thereby forming spaced discontinuous streams thereof mixed with primary air insuffient to ensure complete combustion of the fuel into the combustion chamber of the tunnel kiln, and introducing larger amounts of secondary air for maintaining and completing combustion into the combustion chamber in streams spatially separated from and substantially parallel to the streams of admixed fuel and primary air.

7. In a tunnel kiln, the combination of a vertical wall of the combustion chamber of the kiln, devices arranged in said wall for introducing pulses of fuel along substantially predetermined paths for burning in said combustion chamber, and means arranged in said wall for introducing combustion-maintaining gas into said combustion chamber, said devices and said means being spatially separated from and alternating with each other.

8. In a tunnel kiln, the combination of a vertical wall of the combustion chamber of the kiln, devices arranged in said wall for introducing pulses of fuel into a first set of spaced zones provided in said combustion chamber, and means arranged in said wall for introducing combusdon-maintaining gas into a second set of zones interdigitated between ones of said first set in said chamber, said first and said second set ofzones being separated from one another by partition means each having at least one small communicating orifice.

9. In a tunnel kiln, the combination of a vertical wall of the combustion chamber of the kiln, a baking truck in said combustion chamber and having a space below said baking truck, partition walls dividing said space into individual ducts, devices arranged in said wall for introducing fuel substantially horizontally into alternate ducts, and means arranged in said wall for introducing combustion-maintaining gas into other alternate ones of said ducts, said other alternate ducts alternating with said first alternate ducts and said partition walls having orifices therein.

References Cited in the file of this patent UNITED STATES PATENTS 824,723 Johnston July 3, 1906 1,062,606 Ramen May 27, 1913 1,683,309 Selliez Sept. 4, 1928 1,900,223 Burke Mar. 7, 1933 2,386,835 Beatty Oct. 16, 1945 2,982,530 Drakengren May 2, 1961 FOREIGN PATENTS 1,261,890 France Apr. 17, 1961 

1. A METHOD OF HEATING TUNNEL KILNS WHICH COMPRISES INTRODUCING PULSES OF FUEL THEREBY FORMING SPACED DISCONTINUOUS STREAMS THEREOF WITHOUT SUBSTANTIAL ADMIXTURE OF A COMBUSTION-MAINTAINING GAS INTO THE COMBUSTION CHAMBER OF THE TUNNEL KILN, AND INTRODUCING GAS FOR MAINTAINING COMBUSTION INTO THE COMBUSTION CHAMBER IN STREAMS SPATIALLY SEPARATED FROM AND SUBSTANTIALLY PARALLEL TO THE STREAMS OF FUEL. 